/*
 * Copyright 2012 The Netty Project
 *
 * The Netty Project licenses this file to you under the Apache License,
 * version 2.0 (the "License"); you may not use this file except in compliance
 * with the License. You may obtain a copy of the License at:
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
 * License for the specific language governing permissions and limitations
 * under the License.
 */
package io.netty.channel.socket.nio;

import io.netty.channel.ChannelException;
import io.netty.channel.ChannelMetadata;
import io.netty.channel.ChannelOption;
import io.netty.channel.ChannelOutboundBuffer;
import io.netty.channel.nio.AbstractNioMessageChannel;
import io.netty.channel.socket.DefaultServerSocketChannelConfig;
import io.netty.channel.socket.ServerSocketChannelConfig;
import io.netty.util.internal.PlatformDependent;
import io.netty.util.internal.SocketUtils;
import io.netty.util.internal.logging.InternalLogger;
import io.netty.util.internal.logging.InternalLoggerFactory;

import java.io.IOException;
import java.net.InetSocketAddress;
import java.net.ServerSocket;
import java.net.SocketAddress;
import java.nio.channels.SelectionKey;
import java.nio.channels.ServerSocketChannel;
import java.nio.channels.SocketChannel;
import java.nio.channels.spi.SelectorProvider;
import java.util.List;
import java.util.Map;

/**
 * A {@link io.netty.channel.socket.ServerSocketChannel} implementation which uses
 * NIO selector based implementation to accept new connections.
 */
public class NioServerSocketChannel extends AbstractNioMessageChannel
    implements io.netty.channel.socket.ServerSocketChannel {
  
  private static final ChannelMetadata METADATA = new ChannelMetadata(false, 16);
  private static final SelectorProvider DEFAULT_SELECTOR_PROVIDER = SelectorProvider.provider();
  
  private static final InternalLogger logger = InternalLoggerFactory.getInstance(NioServerSocketChannel.class);
  
  private static ServerSocketChannel newSocket(SelectorProvider provider) {
    try {
      /**
       *  Use the {@link SelectorProvider} to open {@link SocketChannel} and so remove condition in
       *  {@link SelectorProvider#provider()} which is called by each ServerSocketChannel.open() otherwise.
       *
       *  See <a href="https://github.com/netty/netty/issues/2308">#2308</a>.
       */
      // todo open selector channel
      return provider.openServerSocketChannel();
    } catch (IOException e) {
      throw new ChannelException(
          "Failed to open a server socket.", e);
    }
  }
  
  private final ServerSocketChannelConfig config;
  
  /**
   * Create a new instance
   */
  public NioServerSocketChannel() {
    this(newSocket(DEFAULT_SELECTOR_PROVIDER));
  }
  
  /**
   * Create a new instance using the given {@link SelectorProvider}.
   */
  public NioServerSocketChannel(SelectorProvider provider) {
    this(newSocket(provider));
  }
  
  /**
   * Create a new instance using the given {@link ServerSocketChannel}.
   */
  public NioServerSocketChannel(ServerSocketChannel channel) {
    // todo 这里定制 OP_ACCEPT
    // todo 注册 OP_ACCEPT accept 事件
    super(null, channel, SelectionKey.OP_ACCEPT);
    // nio server socket config
    config = new NioServerSocketChannelConfig(this, javaChannel().socket());
  }
  
  @Override
  public InetSocketAddress localAddress() {
    return (InetSocketAddress) super.localAddress();
  }
  
  @Override
  public ChannelMetadata metadata() {
    return METADATA;
  }
  
  @Override
  public ServerSocketChannelConfig config() {
    return config;
  }
  
  @Override
  public boolean isActive() {
    // As java.nio.ServerSocketChannel.isBound() will continue to return true even after the channel was closed
    // we will also need to check if it is open.
    return isOpen() && javaChannel().socket().isBound();
  }
  
  @Override
  public InetSocketAddress remoteAddress() {
    return null;
  }
  
  @Override
  protected ServerSocketChannel javaChannel() {
    return (ServerSocketChannel) super.javaChannel();
  }
  
  @Override
  protected SocketAddress localAddress0() {
    return SocketUtils.localSocketAddress(javaChannel().socket());
  }
  
  @Override
  protected void doBind(SocketAddress localAddress) throws Exception {
    if (PlatformDependent.javaVersion() >= 7) {
      javaChannel().bind(localAddress, config.getBacklog());
    } else {
      javaChannel().socket().bind(localAddress, config.getBacklog());
    }
  }
  
  @Override
  protected void doClose() throws Exception {
    javaChannel().close();
  }
  
  @Override
  protected int doReadMessages(List<Object> buf) throws Exception {
    //接受新连接创建SocketChannel
    SocketChannel ch = SocketUtils.accept(javaChannel());
    
    try {
      if (ch != null) {
        buf.add(new NioSocketChannel(this, ch));
        return 1;
      }
    } catch (Throwable t) {
      logger.warn("Failed to create a new channel from an accepted socket.", t);
      
      try {
        ch.close();
      } catch (Throwable t2) {
        logger.warn("Failed to close a socket.", t2);
      }
    }
    
    return 0;
  }
  
  // Unnecessary stuff
  @Override
  protected boolean doConnect(
      SocketAddress remoteAddress, SocketAddress localAddress) throws Exception {
    throw new UnsupportedOperationException();
  }
  
  @Override
  protected void doFinishConnect() throws Exception {
    throw new UnsupportedOperationException();
  }
  
  @Override
  protected SocketAddress remoteAddress0() {
    return null;
  }
  
  @Override
  protected void doDisconnect() throws Exception {
    throw new UnsupportedOperationException();
  }
  
  @Override
  protected boolean doWriteMessage(Object msg, ChannelOutboundBuffer in) throws Exception {
    throw new UnsupportedOperationException();
  }
  
  @Override
  protected final Object filterOutboundMessage(Object msg) throws Exception {
    throw new UnsupportedOperationException();
  }
  
  private final class NioServerSocketChannelConfig extends DefaultServerSocketChannelConfig {
    private NioServerSocketChannelConfig(NioServerSocketChannel channel, ServerSocket javaSocket) {
      super(channel, javaSocket);
    }
    
    @Override
    protected void autoReadCleared() {
      clearReadPending();
    }
    
    @Override
    public <T> boolean setOption(ChannelOption<T> option, T value) {
      if (PlatformDependent.javaVersion() >= 7 && option instanceof NioChannelOption) {
        return NioChannelOption.setOption(jdkChannel(), (NioChannelOption<T>) option, value);
      }
      return super.setOption(option, value);
    }
    
    @Override
    public <T> T getOption(ChannelOption<T> option) {
      if (PlatformDependent.javaVersion() >= 7 && option instanceof NioChannelOption) {
        return NioChannelOption.getOption(jdkChannel(), (NioChannelOption<T>) option);
      }
      return super.getOption(option);
    }
    
    @SuppressWarnings("unchecked")
    @Override
    public Map<ChannelOption<?>, Object> getOptions() {
      if (PlatformDependent.javaVersion() >= 7) {
        return getOptions(super.getOptions(), NioChannelOption.getOptions(jdkChannel()));
      }
      return super.getOptions();
    }
    
    private ServerSocketChannel jdkChannel() {
      return ((NioServerSocketChannel) channel).javaChannel();
    }
  }
  
  // Override just to to be able to call directly via unit tests.
  @Override
  protected boolean closeOnReadError(Throwable cause) {
    return super.closeOnReadError(cause);
  }
}
